1. Field of the Invention
The present invention is directed towards a navigation light system for watercraft, and more particularly towards a navigation light system that employs spatially separated partial arc lights which are collectively the optical and functional equivalent of existing navigation running lights.
2. Description of the Related Art
Navigation lights are required for operation of a boat at nighttime. The United States Coast Guard has established Navigation Rules for these lights. These Navigation Rules are also published by the American Boat and Yacht Council in Section A16 of their handbook. Section A16 illustrates these lights as emitting a beam of light shaped as a radial wedge of light shining out across the water surface. Each type of light fixture shall emit light of a certain color and intensity over a prescribed horizontal arc and over a prescribed vertical arc of an intensity to be visible by an observer located at a prescribed distance relative to the watercraft. The rules recognize the physical constraints of mounting these light fixtures and the necessity for other appurtenances and hardware on the boat and therefore allow for some hardware to be placed in the beam of light as long as the hardware does not interrupt more than 6 horizontal degrees of the light beam. This interruption of the light beam is called occlusion. Some occlusion is permitted, but it is undesirable.
Occlusion, or occluding is the undesirable process whereby the beam of light is blocked from its desired or otherwise intended outward path by striking parts of the boat or people that are standing in the way of the light beam. Occlusion of the beam is detrimental to both the operators of the boat and to distant observers of the boat. It is detrimental to the operators of the boat because the light striking the occluding object reflects back towards the operator and causes glare in his eyes that reduces his night vision capability. It is also detrimental to a distant observer of the subject boat because the allowed occlusion obliterates the very same light that the distant observer needs to see in order to inform him of the presence of the subject boat and take necessary evasive action. Occlusion and glare are often the unavoidable result of using only one light centrally located on the boat and is a common problem on most boats. Even the use of two lights as directed by the Navigation Rules causes glare and occlusions.
The Navigation Rules have recently imposed a caveat that required navigation running lights be mounted in a fashion to minimize glare and maximize brightness. These two goals are couched in regulatory lexicon of “maintain proper lookout” (which is intended to minimize glare as perceived by an operator) and “maintain conspicuity” (which is intended to increase light brightness and maintain a continuous display as perceived by a neighboring boat). The Navigation rules do not explicitly use the term “running light” but instead uses the term “underway” to define which lights are required when a watercraft or vessel is not at anchor, or made fast to the shore, or aground (definition of “underway” according to Rule 3(i) of the General Definitions). As used herein, the term “running light” is intended to mean those lights that are required to remain on while the watercraft or vessel is underway as understood within the definitions of the Navigation Rules.
The Rules for the beam spread requirement for each of the different navigation running lights has some similarities for the different running lights. As used herein, the beam spread of a navigation running light is defined in terms of “sectors” including vertical sectors and horizontal sectors. The vertical sector is the included angle of emission of the light outwardly from the boat as declared by the upper and lower limits of the angle relative to an external reference, wherein the external reference is generally the horizontal plane. For example, the Rules state that at least the required minimum intensity is maintained at all angles from 5 degrees above to 5 degrees below the horizontal and at least 60 percent of the required minimum intensity is maintained from 7.5 degrees above to 7.5 degrees below the horizontal. Basically, the Rules require the vertical sector to be +/−5 degrees from the horizon and tapering off to a minimum of +/−7.5 degrees, but do not specifically refer to a maximum angle. Practical lights should have increased vertical sectors since the watercraft may lean from side to side while underway. This is particularly true for sailboats that lean way over while underway, so that the vertical sector for sailboats should be larger than for powerboats, e.g., +/−30 degrees. The horizontal sector is the included angle of emission of the light outwardly from the boat as declared by the forward and rearward limits of the angle relative to an external reference, wherein the external reference is the front to rear centerline of the watercraft. Masking is typically defined by the term “screens” and that is usually part of the fixture or an adjacent part of the boat, e.g., the hull. For example, the vertical beam spread is 7.5 degrees above the horizon to 7.5 degrees below the horizon for all navigation running lights. However, the horizontal beam spread for the red and green side marker lights is 112.5 degrees for each of the lights. The horizontal beam spread for the masthead light is two times 112.5 degrees, or 225 degrees centered about the straight-ahead direction of the boat. The beam spread for the steaming light is 225 degrees centered about the straight-ahead direction of the boat. The beam spread for the stern light is 135 degrees centered about the straight behind direction. The beam spread for the all-around light is 360 degrees, and is configured as the consolidation of the masthead light, or the steaming light, and the stern light into one fixture. As a convenience for discussion for a navigation light system according to the present invention, the horizontal beam spread is referred to as the horizontal sector and the vertical beam spread is likewise referred to as the vertical sector.
The angle of 112.5 degrees comes from an archaic concept. The Navigation Rules require that the red and green side marker lights start at straight ahead and end at a back angle of “two compass points abaft of athwart ship.” What this meant to old sailors was that the red and green lights had to extend from straight ahead to around on each side of the boat to slightly behind each shoulder. The term “athwart ship” means directly out to the sides at 90 degrees from the longitudinal centerline of the boat. The term “abaft” means toward the rear, or “aft”, end of the boat. To better define the angle, it was expressed in terms to which they could relate which was the dial of a compass. There are 32 points on a compass dial. One compass point is 11.25 degrees because there are 32 directional points on the dial of a compass. This is calculated by dividing 360 degrees by 32 points, and therefore equals 11.25 degrees per point. At 90 degrees to the left of the straight ahead direction is the port side and is called the port side athwart ship. The old sailor's left shoulder was at the port side athwart ship. Therefore, “two compass points abaft of athwart ship” is 90 degrees plus another 22.5 degrees, which equals 112.5 degrees, and is the required cutoff point for the port side marker lights and the masthead lights. Similarly, the starboard side cutoff is two compass points abaft of the starboard side athwart ship direction. The starboard cutoff line is 112.5 degrees to the right of straight ahead. The precision of the arithmetic is unfortunate because it forces the designers of these lights to direct their attention to a falsely precise number and often disregard the consequences of glare and occlusion.
It was probably not intended that this cut-off angle be enforced with blind determination. But more likely this cut-off angle was selected as an angle to which old sailors could relate to the course direction of a neighboring boat. Therefore, it allowed an operator who sees the red or green lights of a neighboring boat to be aware of possible collision due to closing paths. Whereas, if the red or green lights are not visible, the observed boat is on a departing heading and collision is less imminent. At night, the human eye cannot discern angles within a half of a degree of precision. In fact, it takes a very special person to be able to discern 15 degrees. Rigorous pursuit of such minutia often leaves unsolved the larger issues of visual safety as it relates to conspicuity and proper lookout.
Also of historical interest is the permitted use of a single “360 degree” or “all around light” as a suitable substitute for the required 225 degree masthead light plus the 135 degree stern light. This substitution of one light for two lights is permitted in accordance with the Navigation Rules, on boats less than 12 meters in length. This was done as a convenience and cost saving measure for the benefit of small boats. Thus, the use of a single light is considered the functional equivalent of two spatially separated lights where each light satisfies the concept of a piecewise continuous partial presentation to an observer. And by deduction, the converse is also true as this fact is the basis for allowing the 360 degree light. That is to say, piecewise continuous partial arc lights are functionally equivalent to a single light. They are functionally equivalent because they are optically equivalent. Often better.
Although the Navigation Rules show single fixtures, there is no real valid scientific basis as to why these different lights cannot be configured differently and still be optically equivalent to the original standard as prescribed by the Navigation Rules.
It is a reality of three-dimensional spatial geometry that when viewing navigation lights, visual separation always means there is spatial separation, but spatial separation does not always mean there is visual separation. This is because two spatially separated points of light in a darkened, three-dimensional field can be rotated to appear to visually merge, that is to appear to have no visual separation. Conversely, two spatially merged points of light cannot be rotated to appear to be visually separated. This is one of the precepts of geometry in three-dimensional space.
Safe operation of a boat at night requires that an operator be able to see and that the boat be seen. This is a double requirement. The first goal is to design the lighting system so as to reduce the glare that impairs an operator's ability to see out into the darkness. The second goal is to increase the brightness of the lights on a boat such that an operator's boat can readily be seen by a distant observer. This ability to be seen is reduced by the problem of occlusion in prior art.
All types of glare are detrimental to an operator's ability to see. There are at least five types of glare. There is primary glare, secondary glare, reflected glare, re-reflected glare, and bloom. Primary glare is light that is emitted straight from the filament of a lamp. Secondary glare is light that is emitted from the lens of a light fixture wherein the light is that portion which is deflected away from the desired direction designed as part of the intent of the fixture. This secondary glare is easily observed as the light spilling off the lens of a flashlight when the light is observed from slightly ahead of the light, but off to the side of the light beam. Secondary glare is the source of much of the glare problem associated with navigation light installation and operation. Reflected glare is light that strikes an object somewhere in the view of the operator and reflects back into an operator's eyes. Re-reflected glare is light that strikes an object somewhere in the view of an operator and wherein the light is emanating from another reflective surface. Bloom is caused by light that strikes particles in the air such as mist or dust, and causes the air to glow from the light. Fog is a primary cause of bloom.
The diagrams of light beams as presented by the regulatory authorities are over simplifications of classical lens theory. These diagrams do not take into account the difference between lens theory and lens reality. Real life lenses all exhibit diffusion and less than perfect transmission and refraction. These realities give rise to these sources of fugitive light. Fugitive light is any light that goes where it is not wanted and usually causes harmful glare. This harmful glare impairs an operator's ability to see. An operator is not limited to the driver, but may include anyone who contributes to visual look out, and may include even a passenger who casually looks out into the darkness.
The second requirement of nighttime boat operation is that the boat shall be capable of being seen by a distant observer. This requirement is stated as the need to maintain conspicuity. It is obvious that the brighter the lights are on a boat, the more conspicuous it is. However, it would be counterproductive to make the navigation lights so bright that they excessively contribute to the glare problem and thus impair the operator's ability to see. There are regulatory limits on the minimum and maximum brightness of navigation lights. The minimum brightness requirement is to ensure that a distant observer can see the boat. The maximum brightness limit is imposed so that these lights do not temporarily blind an oncoming boat. These limits prohibit the use of docking lights and spotlights while normally operating on the water. However, these limits do allow the non-steady use of searchlights that are manually controllable and do not present a continuous blinding effect to an oncoming boat. There is also a practical limit on the maximum brightness because if a light is too bright, it tends to cause too much glare to the operator and it uses an excess of power.
The physiology of the eyeball is such that even very low levels of light in a person's field of vision, even in the periphery, cause a severe reduction in the ability to see in the darkness. The eye has photoreceptors called rods that are located predominately on the periphery of the retina. These rods are extraordinarily sensitive to low levels of light and tend to over emphasize the effect of peripheral sources of glare. The center of the retina, called the fovea, is saturated with photoreceptors called cones that respond primarily to colors and detail discrimination. This is why people see ghosts out of the corner of their eye, but loose sight of the ghost when they look directly at it. It disappears like a ghost. This is also why it is desirable to configure a lighting system that eliminates even small sources of glare, even those located off to the side of, or above or below, the normal direction of view.
One problem with prior art lights is glare. Excessive glare is usually caused by the placement of a navigation light somewhat centrally located in the boat such that fugitive light casts downward into the cockpit and deck areas of the boat and tends to adversely affect the boat operators ability to see at night. Excessive glare is also caused when the intended and outwardly directed light beam strikes objects or people on the subject boat. In either case, excessive glare is undesirable because it impairs the boat operator's ability to see into the darkness of night as part of his requirement to “maintain proper lookout”. Glare can be reduced or eliminated by proper placement of spatially separated, piecewise continuous, partial arc white lights.
The problem with glare is so severe that it causes some boaters to shut off their lights while running at night. Even though this practice is illegal and dangerous, it is a risk taken by the operator who is desperate to eliminate glare. Running with no lights, or “running dark”, is fairly common in relatively deserted areas such as coastal waters or rivers where it is important for the operator to fully see navigation hazards or navigation aids. The operator calculates the risks and judges that the benefits outweigh the consequences. The operator considers this practice of running with the light off to be less dangerous than running with his lights on, irrespective of what the law dictates. Other operators will stand up to intentionally block the rear mounted, yet forward directed light from striking the foredeck and causing glare. This intentional occlusion of the light is dangerous because a neighboring boat directly ahead cannot see the subject boat. Although it is dangerous, it is usually not illegal for an operator or a passenger to occlude his own light.
A second problem with prior art lights is occlusion. Occlusion is usually caused by the placement of a navigation light somewhat centrally located in the boat and whereby the objects or people in the boat block the outwardly directed light beam from being seen by a distant observer. Thus, the subject boat cannot be seen at all times from all angles and therefore does not meet the requirement to “maintain proper conspicuity”. Occlusion can be reduced or eliminated by proper placement of spatially separated, piecewise continuous, partial arc white lights.
Prior art navigation lights use a single lamp inside a fixture. The lamp is usually an incandescent type with a tungsten filament inside a glass globe. This lamp is covered by a lens that protects the globe and gives red or green color when needed, to the white light emitted from the filament. Various lamp wattage and luminosity is available for a full range of applications.
Light Emitting Diode (LED) technology has provided an alternative to the incandescent lamp. LED's are often bundled together in a single fixture and oriented to meet the horizontal beam spread required of navigation lights. Current production LED's have a clear plastic encapsulation to protect the individual emitting substrate of the chip. The encapsulation is usually shaped as a convex lens to focus the light from the chip surface into a cone of light. This cone of light has a slight cylindrical divergence about the central axis. Thus the beam spread is fairly narrow. Therefore, several LED's need to be ganged together like knuckles on a clenched fist so that each LED element can broadcast outwardly over a fairly narrow fan of light, but taken collectively, the total angle is sufficiently wide to meet the horizontal beam spread as required by the Navigation Rules. The use of Light Emitting Diode (LED) technology is becoming popular, however they have a fairly narrow beam spread which is disadvantageous when used in single fixture navigation light systems, but can be advantageous in a navigation light system according to the present invention. Prior art using LED's requires that the individual elements be clustered in a divergent array in order to attain the full horizontal beam spread requirement. Whether the light is incandescent or LED or any other source, it is the wide angle of divergence of the beam spread of prior art lights combined with a bad location of the light fixture that causes glare on the boat and appurtenances.
U.S. Pat. No. 6,637,915 to Von Wolske (hereinafter “Von Wolske '915”) describes a system and method that utilizes separate fixtures on the stern light to provide full coverage using two fixtures. This is done to provide full angular coverage around obstructions on the transom like outboard motors and outdrives. Von Wolske '915 also uses two half-angle masthead light fixtures to facilitate mounting on either side of the longitudinal centerline. These two fixtures provide full angle coverage as required of a masthead light.
Conventional sailboats lights show a single masthead light located fairly high on the mast. This high location renders the light rather ineffective because, by nature, people look at the horizon for danger. A light located high on a mast is suitable for high seas operation, but is less than ideal for use on inland lakes surrounded by hills or high banks. The hills or high banks often have house and street lights that tends to confuse the boater and delude him into believing that the masthead light on the sailboat is merely a shore based light and of no consequence. Prior art does not give suitable close proximity warning to an approaching boat.